How to scroll to middle of page (with jquery)

Hello experts
I 'm using a function to add a new div onclick loading the content with an ajax call.
The problem is that i cant scroll the new div to the middle of the page.
Below my code.
Any help to fix this?

// JavaScript Document
 $('#adddiv').live('click', function () {
   $.ajax({
     type: "POST",
     url: "thisfunction.cfc?returnformat=json",
     data: {
       method: 'fgetinstruction'
     },
     success: function (f) {
       var formattedResponse = $.parseJSON(f);
       if (jQuery.isArray(formattedResponse) === true) {
         var success = formattedResponse[0]['success'];
         var content = formattedResponse[0]['content'];
         var newid = formattedResponse[0]['newid'];
         if (success === true) {
           $(content).appendTo(instruc);
           $('#' + newid).scrolltocenter();
           return false;
         }
       }
     }
   }, "json")
 });
 jQuery.fn.scrolltocenter = function () {
   var scrollto = this.offset().top + (this.height() / 2);
   this.animate({
     scrollTop: scrollto
   });
   return this;
 }

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